INTRODUCTION.

SN 1993J appeared in NGC 3031 (M81) , a galaxy located in Ursa Major , 12 m.l.y. far away from us, has been one of the brightest an best studied SNe of the modern Astronomy.

• It has been the brightest SN appeared in the northern Hemisphere in the latest 21 years.
• This is probably the SN with a more exact knowledge about the right moment of the explosion.
• It has been monitored and studied by the most sophisticated professional telescopes, this includes Hubble, M. palomar , Roque de los Muchachos , and VLA telescopes, and Rosat , Asca, IUE.... Satellites..

SN 1993J was discovered on the 28th of March , Sunday night , By Francisco Garcia Díaz , amateur astronomer living in Lugo , Spain with a 10" telescope. Francisco is an active member of M1.

This group was created five years ago by M.A.A. members Diego Rodriguez , José Ripero and Francisco Pujol. Since the very begining we were aware that to find a SN was an extremely difficult task, but there was Robert Evans example , amateurs astronomer with 26 discoveries . This fact encouraged us to keep observing and try to find a new small point not included in the M. Palomar images or in the Thompson Bryan charts.

The group gathered botch , equipment and bibliography to do SN hunting ( RealSky Thompson-Bryan charts , CCD Buil-Thouvenot , and Lopez Alvarez Atlases, etc...) We also own a computer program able to provide asteroid appulses to deep-sky objects , and therefore , to clarify possible false alarms due to asteroids.

Francisco Garcia , joined the group three years ago. In the five years prior to the discovery we achieved 25.000 negative observations checking 650 different galaxies . We have also been able to observe and monitor visually , photographically and with CCD , SN 1989 in M66 , (This SN was one of the reasons to create the group ), SN 1991T in NGC 4527 , SN 1991X in NGC 4902 and SN 1992G in NGC 3294.

Chronology of the discovery of SN 1993J in M 81

• Sunday, 28th of March 1993

Francisco García , member of the SN Search Group M1 , observed a suspected star in the galaxy NGC 3031 (M81) , located in Ursa Major , He estimated it to be m=11.8 . He called inmediately Jose Carvajal , M1 member also , asking him to verify in the Asteroids Appulses computer program , whether there was an asteroid.While Francisco Observes again the galaxy , Jose Carvajal calls Diego Rodriguez, another M1 members , asking him to take a CCD image of the galaxy and thus , to confirm that the suspected new star was present. In that position nothing appeared in the Thonson Bryan , Buil-Thouvenot and Hubble Atlases. Diego Rodriguez called Enrique Pérez, Spanish astronomer astronomer observing that night with 2.5 meters aperture Issaac Newton Telescope , in the Roque de los Muchachos Observatory in Canary Island. Enrique replied he was not sure whether he would be able to confirm the SN .

• Monday, 29th of March 1993

The twilight of Monday 29th , found Diego Rodriguez , Francisco Pujol , Francisco Garcia , and José Ripero , waiting anxiously , the first star of the night to confirm the suspected new SN... Actually , the star was in the same position and showed a brightness of m=11 , estimations were made both , visually and with CCD .

After this confirmation we called urgently Dr. Wamsteker , Scientific Director of VILSPA , we also sent him by Fax a copy of the CCD image taken by Diego Rodriguez. Afterwards we called Janet Mattei (AAVSO) to confirm the SN . Finally we talked to our good Australian Friend Rovert Evans the amateur with more SNe decoveries. In the same night , a few hours late , the first spectrum of the SN was taken by Enrique Pérez in the 2.5 meters aperture Isaac Newton Telescope.

• Wednesday, 31th of March 1993

Early in the morning we received , at last , The IAU Circular 5731 announcing the discovery of SN 1993J by Francisco Garcia -Diaz of Lugo Spain , and the SN group M1 of Madrid Astronomical Association. El PAIS , the most important Spanish newspaper , covers the information , and remarks the importance of this event discovered by Madrid amateurs astronomers.

Important highlights of this covery

There are a few aspects to be pointed out related to this discovery:

1.-The very short time that elapsed between the visual discovery and the CCD image.This became crucial to know the exact SN position , and thus , to make easier the spectral confirmation by professional telescopes.

2.- We were also very fast confirming this was neither an asteroid , nor a variable star lurking near the galaxy, Just a few minutes after the first sight , it had already been confirmed by another observer.

3.- A second visual confirmation , performed 24h later by most M1 members definitely assured this star was a real SN.

4.- All this was possible due to the existence of an organized team with good experience and resources to go ahead without doubst in case a SN arises.

Importance and peculiarities of SN 1993J

The following reasons make SN 1993J very peculiar:

This SN appeared in very close galaxy . Whit the exception of SN 1987A , found in the Large Magellenic Cloud , modern Astronomy has never aimed its telescopes to a so near SN.

The explosion time is known with just a few hours of uncertainty . Actually , there is a photographic observation performed on saturday ,27th of March , at 21h45 (UT) . In the picture take by the French amateur J.C. Merlin , nothing brigther than m=16 appeared in the SN position .

On Sunday 28th of March , A.W. Neely , American amateur took some CCD images at 7h15 (UT) . At this time the SN was already present and showed a brightness of m=13.7 .

On Sunday 28th of March , at 21h45 (UT) , Francisco Garcia made discovery and estimated the SN to be at m=11.8

According to last news sent By Dr. de Vaucouleurs , professional astronomers consider explosion began on the midday of saturday 27th of March. This assumption is based on theoretical models about the evolution of the SN brightness . For this calculation it is assumed that the initial brightness of the  progenitor  star should be m=20.8

SN 1993J showed twon  maximum  of light. The first happened one day after the discovery , while the second one occurred three weeks later.

A nearly unique spectral behaviour . SN 1987K appeared in NGC 4651 (Virgo) , and SN 1993J in M81 , are the only ones that moved from type II when the explosion , to type Ib , some time later . Therefore , SN 1993J represents a repetition of very unusual behaviour.

SN 1987K was discovered by Berkeley Automated SN Search Group , led by Pennypacker , in late July 1987 ; this SN achieved m=14.2 . Based on its spectrum , it was initially classified as type II (plateau) to a type Ib . Actually , in the spectrum taken on May 11 1993 , all alfa hydrogen lines had vanished . According to Astrophysic theories , wide and clear oxigen an calcium lines will fill the spectrum in the coming weeks.

Progenitor star mass has been estimated to be in the rage of 10-20 M.O.

recognitions.

To Dr. Wilhem Wamsteker , Director of Villafranca Tracking Station, (VILSPA), and to all his team.

To Mrs. Janet Mattei , AAVSO Director , she helped us a lot spreading through electronic-mails the new of our discovery to most Observatories and Universities.

To SNe Group ,of IAC (Intituto Astrofisica de Canarias), conducted by Dr . Mr. Francisco Sánchez , and specially to Mr . Gaby Gómez , member of this group , for the continuous information provided about the behaviour of SN 1993J.

To all wives , mothers, girlfriens , sons and daughters ... of M1 group members , to bear our madness until the new about the discovery arrived . And obviously , to share their lives with us and with SN 1993J . We are in debit for your understanding and help...

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